The present invention relates generally to methods for chemically bonding two dissimilar polymers. More particularly, it is directed to a method for providing covalent bonding between a polymeric prosthetic device and polymethylmethacrylate bone cement.
Numerous surgical procedures are available for the reconstruction and/or repair of bones. Many such methods involve the use of prosthetic devices produced from polymeric materials such as polyethylene. Indeed, a variety of polymeric prostheses are commercially available for use in repairing damaged hip joints, knee joints etc., due to such diseases as osteoarthritis, rheumatoid arthritis, traumatic arthritis, avascular necrosis, sickle cell anemia and osteoporosis.
The most common technique for reconstructing damaged bone tissue involves initially cutting and drilling the bone so that it conforms to the shape of the securement portion of a prosthesis. A number of shallow holes are generally drilled or cut into the surfaces of the bone tissue adjacent to the prosthesis in order to form projecting cavities into which bone cement can flow so as to form a strong mechanical interlock between the cement and the bone tissue.
In the majority of such procedures, the prosthesis is secured into place by use of polymethylmethacrylate (PMMA) bone cement. PMMA is a self-curing acrylic resin; it polymerizes at room temperature without any external application of heat. However, PMMA is a "luting" agent, rather than an adhesive, i.e., the cement does not produce any chemical bond with bone tissue to hold the prosthesis in place. Rather, the PMMA fills irregularities in the bone and hardens to form a mechanical interlock. Because the bond so formed is mechanical in nature, preparation and application technique can be very important in the overall success of these procedures. Ineffective bond formation can result in eventual loosening of the prosthesis and failure of the product. This, in turn, results in discomfort to the patient and a need for surgical replacement of the prosthesis.
U.S. Pat. Nos. 5,002,582 and 5,512,329 report methods for the preparation of modified surfaces by covalently bonding polymer molecules thereto by external activation of latent reactive groups, such as photactivatable ketones, carried by the polymer molecules. The polymer molecules are so spatially oriented as to enable one or more of the latent reactive groups to come into covalent bonding proximity with the substrate surface. Upon activation of the latent reactive groups by applying external stimulation, typically ultraviolet radiation, covalent bonds can be formed between the latent reactive group and the substrate.
There is a need in the orthopedic arts for simple and cost effective methods for providing improved adhesion between a prosthetic device and the bone cement to which it is bonded. A great deal of effort and expense has been directed at attempts to provide such improved attachment methods. However, for the most part, these attempts have proved largely unsuccessful and most surgeons continue to utilize PMMA in the manner described above. We provide herein a method for producing prostheses that are attached to bone cement via covalent chemical bonding, resulting in improved bonding strength between a polymeric prosthetic device and bone.